There are a number of techniques for the introduction of genes into cells. One common method involves viruses that have foreign genes (e.g., transgenes) incorporated within the viral DNA. However, the viral genes are also delivered with the desired gene and this can lead to undesirable results.
Nonviral gene delivery systems are being developed to transfect mammalian host cells with foreign genes. In such approaches, nucleic acid is typically complexed with carriers that facilitate the transfer of the DNA across the cell membrane for delivery to the nucleus. The efficiency of gene transfer into cells directly influences the resultant gene expression levels.
The carrier molecules bind and condense DNA into small particles which facilitate DNA entry into cells through endocytosis or pinocytosis. In addition, the carrier molecules act as scaffolding to which ligands may be attached in order to achieve site specific targeting of DNA.
The most commonly used DNA condensing agent for the development of nonviral gene delivery systems is polylysine in the size range of dp 90–450. Its amino groups have been derivatized with transferrin, glycoconjugates, folate, lectins, antibodies or other proteins to provide specificity in cell recognition, without compromising its binding affinity for DNA. However, the high molecular weight and polydispersity of polylysine also contribute to a lack of chemical control in coupling macromolecular ligands which leads to heterogeneity in polylysine-based carrier molecules. This can complicate the formulation of DNA carrier complexes and limits the ability to systematically optimize carrier design to achieve maximal efficiency.
Clearly, there is a need for improved methods of gene delivery. Such methods should be amenable to use with virtually any gene of interest and permit the introduction of genetic material into a variety of cells and tissues.